Glossary term
AST
Also known as: Aspartate Aminotransferase
Part of: Liver Function Tests
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- Written in plain English
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- Reviewed by Medipher Editorial Team
An enzyme found in the liver, muscle and other tissues. It rises when these tissues are irritated or damaged.
Medipher explains medical wording in plain English — it does not diagnose or replace a clinician. If this is a medical emergency, call your local emergency number immediately.
Simple visual explanation
What is this?
AST (aspartate aminotransferase) is an enzyme found in the liver but also in muscle, heart and other tissues. Levels rise when any of these tissues are irritated or injured.
Because it's not exclusive to the liver, AST is usually interpreted alongside ALT — which is more specific to the liver.
Why is it important?
The AST-to-ALT ratio helps clinicians spot patterns — for example, AST higher than ALT can suggest alcohol-related liver strain, while ALT higher than AST is more typical of fatty liver.
Where you'll see it: Liver Function Tests (LFTs).
How doctors use this result
Clinicians may use this result to:
- Interpret liver irritation alongside ALT.
- Look for alcohol-related patterns of liver strain.
- Distinguish muscle from liver causes of raised enzymes.
- Monitor known liver conditions over time.
What's the normal range?
| Adults | typically < 40 U/L |
Ranges vary by laboratory.
Mild elevations are common and often reflect recent exercise, muscle strain or reversible liver irritation.
- Lower than the usual range
- A lower result is also read in context rather than on its own, and is often simply repeated.
- Within the usual range
- A result inside the range printed by the laboratory is generally read as usual for AST at the time of the test.
- Higher than the usual range
- Liver conditions, alcohol, certain medications or muscle injury.
Normal ranges are guides, not verdicts. Interpretation depends on your age, sex, symptoms, medical history, medications and other investigations — which is why your clinician looks at the whole picture rather than a single value.
Common reasons it may be high
Liver irritation
Any cause of liver cell irritation releases AST alongside ALT.
Regular alcohol use
Alcohol tends to raise AST more than ALT, producing a distinctive ratio.
Some medications
Certain drugs affect the liver or muscle and can raise AST.
Muscle injury or intense exercise
AST is present in muscle, so exercise and strains can raise it.
Heart-related causes (uncommon)
AST is present in heart muscle and rarely rises in cardiac events.
Does an abnormal result always mean something is wrong?
Not necessarily. A number that sits outside the printed range is a prompt for interpretation — not a diagnosis.
- A single result rarely gives the full picture — clinicians interpret it alongside your symptoms.
- Your medical history, medications and other blood tests all shape the meaning of one value.
- Small movements just outside the reference range are common and often not concerning.
- Repeat testing over time is frequently more useful than any single number.
What might happen next?
- Repeat testing after 4–8 weeks.
- Further liver tests and, if needed, imaging.
- Review of alcohol, medications and recent exercise.
One result rarely tells the whole story. Clinicians look at your symptoms, medical history, medications and other tests together — and a single value that sits slightly outside the reference range is often normal for you. Repeat testing over time is frequently more useful than any one number. Medipher helps you understand what a result means in plain English, but it cannot diagnose medical conditions or replace advice from a doctor, nurse or pharmacist.
When should I speak to a healthcare professional?
Speak with your GP or another healthcare professional if:
- You've been asked to repeat the test.
- You're experiencing new or worsening symptoms.
- Your clinician has flagged the result as needing follow-up.
- You don't understand your results or feel unsure what to do next.
If you have severe symptoms — chest pain, severe breathlessness, fainting, heavy bleeding or feel very unwell — seek urgent help. If this is a medical emergency, call your local emergency number immediately. Medipher is designed to help explain medical information and is not an emergency service.
Frequently asked questions
Related guides
Commonly confused with
These tests sound similar to AST, but each answers a different question.
- ALTALT sits mostly inside liver cells, so it is the more liver-specific of the pair.
- GGTGGT is often read alongside ALP to help show whether a rise is coming from the bile ducts.
- CK (creatine kinase)CK comes from muscle, and is sometimes checked when AST is raised but the liver looks otherwise unremarkable.
Learning collections
Follow a guided pathway that puts AST in context, step by step.
Still unsure what your result means?
This page explains one medical term. If you have a blood test, GP letter or hospital report, Medipher can explain your entire document in plain English.
- what your results mean
- unfamiliar medical terminology
- what your clinician may be monitoring
- useful questions to ask at your next appointment
Sources
General patient information referenced when writing this page.
- NHS — Blood testsGeneral background
- NICE Clinical Knowledge SummariesGeneral background
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About this page
- Author
- Omer Suliman
- Medical reviewer
- Clinical review pending
Evidence. Written from public patient-information sources including the NHS, NICE and the Association for Laboratory Medicine, and reviewed for plain-English accuracy before publication.
Educational content only. Medipher explains medical language in plain English. It does not diagnose, and it is not a substitute for advice from a doctor, nurse or pharmacist. Read the medical disclaimer.
Nearly there — keep going.
A short summary and recommended next reads are just below.
Continue learning
- Next upALTAn enzyme found mainly in liver cells. It leaks into the blood when the liver is irritated or damaged.
- Next upAbnormal (on a test report)A flag meaning a result differs from what the laboratory or test expected — not a statement about your health.
- Next upAlbuminThe main protein in your blood, made by the liver. It helps keep fluid inside your blood vessels.
This glossary entry is general health information, not medical advice. Medipher explains medical wording in plain English and does not diagnose, provide treatment advice, or replace a GP, doctor, nurse or pharmacist. Always discuss your results with a qualified clinician.